Uric acid nephrolithiasis.

Uric acid nephrolithiasis is typically found in individuals with a low urine pH and a normal concentration of urinary uric acid. Patients with a history of gout are at greater risk of forming uric acid stones, as are patients with obesity, diabetes, or the complete metabolic syndrome. The unifying renal tubular abnormality of these disorders appears to be the excretion of abnormally acidic urine. This article focuses on the relationship of these disorders to the development of uric acid stones. The diagnosis of uric acid stones can be elusive, because pure uric acid stones are radiolucent on plain radiographs. Ultrasound, or preferably noncontrast helical CT scanning, is required for their detection. The treatment of uric acid stones should focus on alkalinization of the urine with citrate or bicarbonate salts. Additional interventions such as increase in fluid intake and decrease in animal protein ingestion are often beneficial. Patients with documented hyperuricemia often require specific therapy to lower serum uric acid concentration and subsequent excretion.